1. Field of the Invention
The present invention relates to a vehicle heater, in particular, a vehicle heater having a heating chamber and a heat exchange chamber, the heating chamber having a rotor connected to a drive shaft to shear viscous fluid and produce heat to heat up circulating fluid flowing in the heat exchange chamber.
2. Description of the Related Art
U.S. Pat. No. 5,573,184 discloses a heater incorporated into a heating device for motor vehicles. The heater, as shown in FIG. 5, is provided with a fixed housing 52, a working chamber 53 therein and a cooling chamber 56 arranged adjacent to the working chamber 53. The fixed housing 52 has a housing cover or lid 52a, a housing floor 52b and an intermediate wall 57. The working chamber 53 and the cooling chamber 56 are defined separately with the intermediate wall 57. The intermediate wall 57 is provided with cooling ribs 57a protruding into the cooling chamber 56. A drive shaft 58 is rotatably supported by a ball bearing 63 on the fixed housing 52. A rotor 54 is fixed to an end of the drive shaft 58 so that the rotor 54 can rotate in the working chamber 53 as an integrated part of the shaft. The working chamber 53 is filled with viscous fluid (e.g., silicone oil) so as to completely cover the gap between outer walls of the rotor 54 and inner walls of the working chamber 53.
An inlet connector 68 and an outlet connector 69 are formed on the housing floor 52b. A coolant (circulating water) flows through heater form the inlet connector 68 to the outlet connector 69.
An engine transmits the drive force to the drive shaft 58 of the heater via an electromagnetic clutch. The rotor 54 integrally rotates with the drive shaft 58 in the working chamber 53. The viscous fluid between the outer wall of the rotor 54 and the inner wall of the working chamber 53 is then stirred to be shared, generating heat as a result of fluid friction. The heat generated in the working chamber is transmitted via the intermediate wall 57 to the coolant flowing through the cooling chamber 56. This coolant is fed to a heat radiator.
The conventional heater has the cooling chamber 56 that is defined by the intermediate wall 57 at the sides of the front wall, the circumferential wall, and the rear wall of the working chamber 53. However, the intermediate wall 57 is not axially and radially aligned with respect to the rotor 54. This makes it difficult, particularly when the rotor 54 is driven at high speed, to keep a slight clearance defined between the outer surfaces of the rotor 54 and the inner wall surfaces of the working chamber 53 constant.
The cooling chamber 56 has a front cooling chamber 56a and a rear cooling chamber 56b which are connected to each other by way of the gap adjacent to the circumferential walls of the working chamber 53. The coolant in the rear cooling chamber 56b flows into and from the front cooling chamber 56a via the gap. However, since the gap has a very small width in the radial direction with respect to the rotor 54, the coolant entered the rear cooling chamber 56a through the inlet connector 68, is not able to easily flow into the front cooling chamber 56b.
In addition, the coolant reached the rear cooling chamber 56b tends to remain therein and hardly flows back to the front cooling chamber 56a. Accordingly, the circulating passage is not sufficient for the coolant to flow from the inlet connector 68 into the outlet connector 69 while flowing through the respective cooling areas equally.
Further, the gap connecting the front cooling chamber 56a with the rear cooling chamber 56b might not be able to maintain its predetermined width because the intermediate wall 57 is not radially positioned with a sufficient accuracy. Therefore, efficient heat exchange between the working chamber 53 and the cooling chamber 56 cannot be expected.